Shorten lang names in wxTranslations, not wxFileTranslationsLoader.

If a catalog with full language name ("fr_BE") doesn't exist,
wxFileTranslationsLoader tries to look for just the base language ("fr")
too. This isn't something specific to wxFileTranslationsLoader, it makes
sense to do it regardless of the loader.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64154 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/translation.h

@@ -111,6 +111,9 @@ public:
     static const wxString& GetUntranslatedString(const wxString& str);
 
 private:
+    // perform loading of the catalog via m_loader
+    bool LoadCatalog(const wxString& domain, const wxString& lang);
+
     // find best translation for given domain
     wxString ChooseLanguageForDomain(const wxString& domain,
                                      const wxString& msgIdLang);